The present invention relates to a coupling arrangement for the coaxial connection of two shafts. In particular, a crankshaft of an internal combustion engine is connected coaxially to an armature shaft of an electric machine. The invention also relates to a method for the mounting of the coupling arrangement.
Various arrangements for connecting an internal combustion engine to an electric machine and a motor vehicle are known from the prior art. In the prior art, use is normally made of belt drives for connecting the crankshaft to the armature shaft. In this case, the belt pulleys serve for compensation of torque fluctuations and for transmission of power without play. The use of the belt drive, and consequently also the non-coaxial arrangement of the electric machine with respect to the internal combustion engine, lead to a bulky construction. Furthermore, the belt drive requires maintenance.
It is an object of the present invention to specify a coupling arrangement for the coaxial connection of two shafts, which coupling arrangement, while being inexpensive with regard to production and mounting, requires little maintenance and operates quietly. It is also an object of the present invention to specify a corresponding method for the mounting of the coupling arrangement. The connection additionally has the task of compensating for coaxiality errors (angular and axial offsets) between the internal combustion engine and electric machine.
The object is achieved by means of the features of the independent claims. The dependent claims relate to advantageous refinements of the invention.
Thus, the object is achieved by means of a coupling arrangement comprising a first shaft, a second shaft and a coupling. The first shaft is in particular a crankshaft of an internal combustion engine in a motor vehicle. The second shaft is in particular an armature shaft of an electric machine. The electric machine is preferably operated as a high-voltage generator for generating electrical energy. Furthermore, the electric machine may also be used as an electric motor for starting the internal combustion engine. The case of the electric machine is preferably connected directly to the crankshaft case or the case of the internal combustion engine. The two shafts are arranged coaxially. This very compact and space-saving arrangement of the internal combustion engine and of the electric machine requires a special design of the coupling. To ensure quiet operation of the coupling with a low maintenance requirement, it is necessary to ensure transmission of power between the two shafts, in particular in both directions of rotation, without play. The coupling therefore comprises at least one motion element and one coupling element. The coupling element is arranged so as to be movable in a circumferential direction and/or in a radial direction. The motion element ensures that the coupling element abuts, or is pressed, against the respective shaft without play in a circumferential direction or a radial direction. Owing to the play-free abutment of the coupling element against the respective shaft, a torque can be transmitted between the two shafts without play.
It is provided in particular that the motion element is a spring and/or a hydraulic pressure chamber. The spring and/or the hydraulic pressure chamber is arranged in the coupling and presses the coupling element against the first or second shaft, so as to permit the play-free abutment and thus also the play-free transmission of power. Axial movements are also possible.
According to the invention, with regard to the exact design of the coupling arrangement, three variants are provided:
In the first variant, the coupling comprises a first toothed shaft, a second toothed shaft and a third toothed shaft. The three toothed shafts form coupling elements. The first toothed shaft is spaced apart from the second toothed shaft. The third toothed shaft is situated between the first toothed shaft and the second toothed shaft. The three toothed shafts are arranged coaxially along the axis of rotation. The first toothed shaft is connected to the second toothed shaft by way of a torsion spring. Accordingly, the first toothed shaft and the second toothed shaft are each connected rotationally conjointly, for example by way of a polygonal formation, to the torsion spring. In this variant, the torsion spring forms the motion element. The torsion spring causes the first toothed shaft to abut without play against the first shaft and the second toothed shaft to abut without play against the second shaft; this is achieved by virtue of the power flow between the two shafts being established via the third toothed shaft.
In particular, it is provided that the first shaft comprises a first shaft toothing and the second shaft comprises a second shaft toothing. The two shaft toothings are, in particular, internal toothings on the crankshaft and on the armature shaft. In the mounted state of the coupling arrangement, the first shaft toothing meshes both with the first toothed shaft and with the third toothed shaft, and the second shaft toothing meshes with the second toothed shaft and simultaneously with the third toothed shaft.
For the compensation of manufacturing-induced errors with regard to axial offset and angle, the toothing is of flank-centered configuration and is of crowned form at both ends of the toothed shaft.
The third toothed shaft is preferably of internally hollow form. In this way, it is possible for the torsion spring to extend through the third toothed shaft. The first toothed shaft and the second toothed shaft are seated on the two ends of the torsion spring. The third toothed shaft is preferably arranged so as to be rotatable relative to the torsion spring.
The first toothed shaft and the second toothed shaft are preferably rotated relative to one another, such that the torsion spring is braced. The first shaft, in particular the first shaft toothing, abuts either against the first toothed shaft or against the third toothed shaft depending on direction of rotation. Likewise, the second shaft toothing may abut either against the second toothed shaft or against the third toothed shaft. The different directions of rotation arise in accordance with whether the electric machine is operated as a generator or as a motor. By virtue of the fact that in each case the tooth flanks of the first toothed shaft and of the third toothed shaft, and of the second toothed shaft and of the third toothed shaft, respectively, are available to the shaft toothings, play-free transmission of power between the crankshaft and the armature shaft is possible.
In the second variant, the coupling is designed as an Oldham coupling. For this purpose, the coupling comprises a main body. The main body comprises a projection on each side. The first projection engages into a groove of the first shaft. The second projection engages into a groove of the second shaft. The projections which engage into the grooves permit, to a limited extent, compensation of a radial and axial offset between the two shafts.
In the second variant, the motion element is preferably a spring and/or a hydraulic pressure chamber. The coupling element is in the form of at least one piston. The piston is guided in a linearly movable manner in the main body. The spring and/or the hydraulic pressure chamber cause(s) the piston to be forced away from the main body. As a result, the piston abuts in the groove of the respective shaft and ensures a play-free transmission of power.
It is provided in particular that at least one piston is provided on that side of the main body which faces toward the first shaft, that is to say on the first projection, and that at least one piston is likewise arranged on the side facing toward the second shaft, that is to say on the second projection.
In a particularly preferred embodiment, in each case multiple pistons are arranged in both projections of the main body. Each piston is subjected to load at least by a spring, and may furthermore be pushed outward by way of a dedicated hydraulic pressure chamber.
Corresponding hydraulic ducts in the main body serve for a supply of pressure to the hydraulic pressure chambers. In particular, the hydraulic pressure from the lubricant supply of the internal combustion engine is used for this purpose.
A preferred check valve in the hydraulic ducts ensures the pressure in the hydraulic pressure chambers below the individual pistons is adequately maintained. It is preferable for small outlet openings to be provided in the pistons. Via said small outlet openings, hydraulic oil emerges from the hydraulic pressure chambers onto the surface of the pistons. This leads to a throttled dissipation of the pressure in the hydraulic pressure chambers, and simultaneously to lubrication of the sliding surfaces between the coupling and the two shafts.
The force of the springs and/or the force of the hydraulic pressure chambers do not need to be of such a magnitude as to constantly force the pistons away from the main body. It is adequate for the pistons to abut against the two shafts at least during a change in the direction of rotation. With increasing torque, the pistons are then pushed into the main body. In this case, the hydraulic oil is conveyed out of the hydraulic pressure chambers to the outside preferably via the outlet openings.
In the third variant, the coupling is in the form of a claw coupling. In this case, the coupling comprises a first ring which is arranged rotationally conjointly on the first shaft, a second ring which is arranged rotationally conjointly on the second shaft, and a compensation ring which is arranged between the two shafts. In this case, the compensation ring constitutes the movable coupling element. The first ring comprises first claws. The second ring comprises second claws. The compensation ring comprises compensation claws. The compensation ring is movable to a limited extent relative to the two shafts. The first claws, the second claws and the compensation claws engage with one another. Limited compensation of a radial and axial offset is thus possible depending on the size of the claws. Viewing the arrangement in a circumferential direction, in each case one compensation claw is situated between a first claw and a second claw. A spring in the form of a helical compression spring or a plate spring is arranged at least between one second claw and one compensation claw. The spring is supported with one end against a second claw and with the other end against a compensation claw. The compensation claw in turn presses against a first claw, whereby said first claw is pressed against a following second claw. The spring thus serves for pressing the second claws against the first claws in the direction of the output effective torque.
In particular, pockets are provided in the compensation claws, such that the springs can be arranged partially in said pockets. In the event of a change in direction of the torque, the springs are compressed to such an extent as to be seated entirely in the pockets. The compensation claws thus abut against the second claws.
For the mounting of the second ring on the second shaft, a conical clamping element is preferably used.
The first shaft is preferably of conical form. An internal cone corresponding thereto is preferably formed on the first ring. A clamping screw and a clamping disk are preferably used in addition to said conical connection. The clamping screw is preferably screwed into the face side of the first shaft, in order thereby to hold the first ring on the first shaft.
The invention preferably encompasses a control unit for the control and/or regulation of the electric machine, wherein the control unit is designed to actuate the electric machine in such a way as to compensate for rotational irregularities. For example, rotational irregularities arise at the crankshaft in a manner dependent on the number of cylinders in the internal combustion engine. These rotational irregularities can be compensated for through corresponding actuation of the electric machine.
The invention furthermore encompasses a method for mounting a coupling arrangement as per the first variant described above. Said method comprises the following steps: (i) bracing the torsion spring by rotating the first toothed shaft relative to the second toothed shaft, (ii) inserting a first rotation prevention means, which fixes the first toothed shaft relative to the third toothed shaft, and a second rotation prevention means, which fixes the second toothed shaft relative to the third toothed shaft, (iii) mounting the first toothed shaft on the first shaft and mounting the second toothed shaft on the second shaft, and (iv) releasing the two rotation prevention means.
In particular, it is preferably provided that the release of the two rotation prevention means takes place at the same time as the first and second toothed shafts are mounted on the first and second shafts. In this case, the rotation prevention means is displaced as a result of the respective toothed shaft being pushed into the internal toothing on the crankshaft or armature shaft. This causes the rotation prevention means to be released.
There are two preferred options for the rotation prevention means: firstly, the rotation prevention means may be in the form of a sleeve. Secondly, the rotation prevention means may be in the form of pins.
The sleeve is pushed on after the bracing of the torsion spring, such that an internal toothing on the sleeve meshes simultaneously with the first toothed shaft and the third toothed shaft, and with the second toothed shaft and the third toothed shaft, respectively. The sleeves are preferably pushed inward when the coupling is mounted on the two shafts. After the mounting process, the sleeves are preferably seated fully on the third toothed shaft. After the mounting process, the sleeves perform no further function but preferably remain on the third toothed shaft.
As an alternative to the sleeves, use may be made of the pins. The pins engage into the face sides of the toothed shafts. After the bracing of the torsion spring, the pins are positioned so as to fix the first toothed shaft relative to the third toothed shaft, and the second toothed shaft relative to the third toothed shaft, respectively such that relaxation of the torsion spring is no longer possible. During the mounting of the coupling arrangement, the pins are displaced, in particular inwardly into the third toothed shaft.
It is also possible for a sleeve to be used as rotation prevention means at one side of the coupling, and for the pins to be used as rotation prevention means at the other side.
For the bracing of the torsion spring, the following method sequence in particular is provided: by rotating the first and/or second toothed shaft, the torsion spring is braced until a desired spring force is measured. It is advantageous to utilize the material plasticization (similarly to expanding screws) for the exact setting of the spring force. The spring force thus remains virtually constant over a wide “tightening angle” and is determined primarily by the spring diameter. The first toothed shaft and/or second toothed shaft are/is thereupon rotated further or backward until the toothings of the three toothed shafts coincide such that the sleeve can be pushed on. If the pins are used, forward or backward rotation is performed until the holes of the pins are aligned, and thus the pins can be inserted.
Further details, features and advantages of the invention will emerge from the following description and from the figures, in which:
Other objects, advantages and novel features of the present invention will become apparent from the following detailed description of one or more preferred embodiments when considered in conjunction with the accompanying drawings.